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A quantitative liquid chromatography mass spectrometry (LC MS) technique was developed to measure the concentrations of heterocyclic nitrogen compounds in ambient fine aerosols (PM2.5). Quadrupole time-of-flight (Q-TOF) MS technology was used to provide both accurate-mass and MS/MS data for confirmation of chemical formula and nitrogen compound structure. The fine aerosol was collected over the winter and summer seasons at an experimental monitoring station at Duke Forest in North Carolina U.S.A. 3-Hydroxypyridine and two beta-carbolines, harmane, and norharmane, were observed in both campaigns at concentrations lower in summer (sum = 332 pg m(-3); N = 27) than winter (554 pg m(-3); N = 31). Aminopyridines, dimethylpyrazoles, and hydroxymethyl-pyridines were observed in the winter aerosols with a total estimated average concentration of 779 pg m(-3). These results demonstrate the possibility of enhanced speciation and provide a first glance at heterocyclic amines in the water-soluble organic nitrogen (ON) fraction of fine aerosols collected from a forest atmosphere. Published by Elsevier Ltd.